This invention relates to a method for producing bi-metal objects, for example, tokens, medallions or commemorative coins.
Methods for producing bi-metallic objects are well-known in the art. For example, plating one metal surface with another by electrolysis or dipping is generally known; and the use of powder metallurgy, that is, subjecting a metal powder to pressure and heat treatment, may be used to form a bi-metal object as described in U.S. Pat. No. 3,499,739.
However, the prior art poses significant problems. First, the area in relief or the image area may not protrude appreciably above the abutting base surface of the object. For example, in producing a bi-metal object by the process of electroplating, it may not be possible to obtain an image area which protrudes more than approximately 125 micro inches above the abutting base surface of the object. And where a higher relief is formed by the process of repeated striking and annealing, the base finish will be unevenly reflective.
Second, a precise regular boundary separating a high relief image area metal from the different metal of the abutting base surface cannot be achieved using methods presently available in the art for producing bi-metal objects.
Third, where sintering is employed in the process for producing the bi-metal object, shrinkage or growth of the dimensions of the object may occur to a degree impractical to predict. Consequently, the dimensions of the final striking die will be difficult to determine with sufficient accuracy to retain the highly desirable sharp border between the two metals.
The present invention provides a method for producing a bi-metal object comprising an area in relief raised significantly higher than 125 micro inches above the base of the object. Moreover, the base of the object will be evenly reflective or will retain a proof finish.
In accordance with the method of the present invention a novel bi-metal object with a highly precise border separating the two constituent metals will be obtained. In addition, the objects will be of uniform dimensions.
Accordingly, it is a general object of the present invention to provide a new and unobvious bi-metallic object as well as a new and unobvious method for producing that object.
More particularly, it is an object of the present invention to provide a new and unobvious bi-metallic object comprising an image area raised appreciably above the abutting base surface of the object.
Moreover, it is an object of the present invention to provide a new and unobvious bi-metallic object comprising an image area separated from the abutting base surface of the object by a sharp and regular boundary.
Another object of the present invention is to provide a bi-metallic object whose base surface abutting the image area will retain a proof finish.
Yet another object of the present invention is to provide a new and unobvious method for producing the bi-metal object of the properties described above.
Other objects will appear hereinafter.